1. Field of the Invention
The present invention relates to a color adjustment method and an image forming system.
2. Description of the Related Art
Heretofore, in the field of the offset printing, a technology has been known, in which solid patches of seven colors RGB and CMYK are printed as control strips on a cut margin, the colors are measured by a densitometer, a colorimeter and the like, and ink amounts of the respective colors are adjusted.
Meanwhile, in an image forming apparatus that performs image formation by using an electrophotographic process, in place of operations of outputting solid patches of four colors CMYK, measuring the colors, and adjusting ink amounts thereof, there is generally performed change of process conditions such as a development potential, which includes adjustment of a charge amount for an image carrier, and adjustment of an amount of light emitting energy to the image carrier. In such a way, adjustment at highest densities is enabled.
In general, when the change of the process conditions is performed as mentioned above, gradation characteristics at half tones are also changed. Accordingly, after the process conditions are changed, gray-scale images of the respective colors CMYK are outputted and are measured, whereby γ correction is performed.
However, in the color adjustment in the image forming apparatus according to the conventional electrophotographic process mode, only primary colors composed of single colors among CMYK are taken as correction targets, and indirect correction is merely performed for secondary or more colors composed of two or more colors among CMYK. In actual, owing to a state change in an imaging process such as transfer and fixing onto a sheet, ideal states are not always achieved in the secondary colors even if the primary colors are adjusted to ideal states. Accordingly, in the color adjustment as described above, stabilization of an image cannot be achieved.
Meanwhile, a chart in which patch images of a thousand or several thousand colors are formed is outputted, the respective patches are individually measured by an external instrument such as the colorimeter, and a color profile is created based on results of the measurement, whereby the color adjustment of the primary color and the secondary or more colors is possible. However, a time and a work load for such color adjustment work are required for a user to an extremely large extent.
While such a technology as described above has been known, Japanese Patent Laid-Open Publication No. H05-153383 discloses a color correction apparatus, which separates density signals of CMY into black components, secondary color components and primary color components, and multiplies each of these separated components by a fixed ratio, thereby performs correction thereof independently, and thereafter, adds and outputs these.
Incidentally, for example, in the field of the light printing, and the like, large-volume printing is performed by using a plurality of image forming apparatuses. Hence, it is necessary that the color adjustment be performed for each of the image forming apparatuses for use so that similar output results can be obtained in all the image forming apparatuses. Then, in the plurality of image forming apparatuses as described above, even if a type thereof is the same, a machine difference is inherent in characteristics of the imaging process, such as transfer properties to a sheet. Accordingly, even if similar color adjustment is performed among the plurality of image forming apparatuses, the same output result is not always obtained.
However, in the technology described in Japanese Patent Laid-Open Publication No. H05-153383, the color adjustment is implemented only for the target apparatus concerned, and how to perform the adjustment among the apparatuses is not taken into consideration at all. Accordingly, it is necessary to perform the color adjustment individually for each of the plurality of image forming apparatuses while comparing the results of the color adjustment among the apparatuses with one another, and this is extremely cumbersome.